provide mechanism to insert steps in the list of steps

[gdementen]

each project should be able to add its own specific steps (ideally without having to redefine the whole list of steps)

• this would allow us to remove the empty steps we currently have inherited from liam2
• this would remove the need to create new commands (e.g. -c, -a) for some of the specific steps we have.
  (eg announce)